An embodiment of the present invention is directed to a method and apparatus for tomosynthesis projection imaging for detection of radiological signs. An embodiment of the present invention can be applied to but not exclusively in the field of medical imaging, the field of non-destructive testing by X-rays and, more particularly, that of mammography. An embodiment of the present invention also relates to an apparatus for mammography comprising a method for image processing.
Mammography is widely used in the detection of lesions and the prevention of breast cancer. The radiological signs associated with these lesions may be either calcium deposits (called microcalcifications) grouped together in a region of space in clusters or opacities. The individual microcalcifications generally form small-sized elements (ranging from about 100 μm to 1 mm in diameter) that are more opaque to X-rays than the surrounding tissues. Opacities are dense regions where the X-rays are absorbed more intensely than in the adjacent regions.
However, it can happen that certain calcium deposits or certain opacities are not spotted. This phenomenon has many causes. In particular, since mammography images are the result of projections, they represent superimposed structures that disturb the visibility of the structures of the breast, and may lead to a falsely positive interpretation
To resolve this problem of positive interpretation, there are mammography methods and apparatus in the prior art that produce a 3D image of the patient's breast. Such a method and apparatus acquires several projections of an object at different angles and thereafter reconstructs the 3D distribution of this object by means of a tomography reconstruction algorithm. The goal then is to detect any lesions that might have been masked during the superimposition of the tissues that takes place during a classic acquisition by mammography projection.
However, this tomosynthesis mammography method and apparatus has drawbacks. In such digital tomosynthesis screening methods and apparatus, a digital volume reconstruction, typically containing 50 to 80 slices, is made for an average breast. Consequently, the quantity of information to be managed is very great. Similarly, access to a piece of information having clinical interest takes much more time since this information is sought sequentially in the volume, side by side.
For present-day mammography method and apparatus, the frequency of use or the rate of medical acts is a vital fact because this frequency comes into play in the economics of the method and apparatus. However, these tomosynthesis mammography methods and apparatus cannot be subjected to high frequency of use because the time of access to information of clinical interest is very great. Furthermore, these methods and apparatus offers no guarantee of screening success since the screening depends on the time taken to locate information of clinical interest.
Another problem, which is more specific to mammography but can, however, occur in other fields, is related to the necessity of being able to analyze certain radiological signs, which become clinically interesting between 100 μm and 1 mm. Since the resolution of the detector is presently 100 μm, a radiologist has to make rapid searches for smaller objects in large volumes.